1 Preliminary results (29.02.2024)

I implemented all the changes we talked about in our last meeting:

  • Instead of manipulating sapStressThreshold we now manipulate height growth (simulated via the browsing module, same browsing probability for all species)
  • New modification levels: size x c(1,2,5,10), frequency x c(1,2,5,10), fecundity x c(1,1/2,1/5,1/10), browsing pressure x c(1,2,5,10)
  • New output: dynamic stand in year 2020, 2050 and 2100
  • Severity for all agents set to 90 % (and 100 for sapling during fire)
  • Fire can only burn cells with a fuel load > 500 kg/ha

I then ran a complete suite of simulations for Berchtesgaden (4 patch size levels * 4 disturbance frequency levels * 4 fecundity levels * 4 browsing levels * 2 climate scenarios * 1 rep = 512 runs)

Here are the results!

1.1 System breaking indicators

Short recap of our indicators:

  1. Structure: basal area decreased by >50 % from reference

  2. Composition: dominant species changed from reference

  3. Remaining forest: stem density dropped below 50 trees/ha

Reference: value under reference conditions (no process modification + baseline climate), calculated for each RU and each year

1.1.1 Indicators over time

Structure changes very quickly until mid of century, then recovers under hot-dry climate, and continues to change under baseline climate, lowest value ~15%

Composition changes continuously for both baseline and hot-dry conditions, lowest value ~50%

Very little forest loss, lowest value ~90 %

1.1.2 Structure compared between the scenarios

Values in year 2100

All processes play a role in structural change, disturbance processes (first row) however seem to have a bigger impact (relatively little change at modification level 1)

More structural change under baseline climate

1.1.3 Composition compared between the scenarios

Values in year 2100

Mainly the disturbance processes (first row) seem to have an impact on compositional change (relatively little change at modification level 1) - especially under modification level 10

Compositional change similar under baseline and hot-dry climate

1.1.4 Forest loss compared between the scenarios

Values in year 2100

Basically only regeneration processes (second row) seem to have an impact on forest loss (relatively little change at modification level 1)

More forest loss under baseline climate

1.2 Spatial patterns

  1. Structure: highest probability of change in higher elevations (left: baseline climate, right: hot-dry climate)

  1. Composition: diffuse pattern

  1. Forest loss: highest probability of change at tree line

1.3 Landscape wide changes

1.3.1 Mean basal area

  • Basal area varied across the simulation period and runs (Dotted red line: simulation with disturbances simulated via modules instead of management):

  • Basal area only consistently dropped below the 2020-value in 2100 once the disturbance rate was increased by more than 25. Under hot-dry conditions it even took a disturbance rate increase of x100.

1.3.2 Species composition

  • Species composition remained relatively stable under reference conditions (= no process modification, first row) and differences between the climate scenarios were small. (Interesting! I would have expected spruce to decrease due to higher temperatures under hot-dry but it still seems to do fairly well without climate change-mediated disturbance change)

  • Under the most extreme scenario (size * 10 + frequency * 10 + fecundity/10 + browsing * 10, second row) spruce decreased while all other species increased - especially larch (makes sense, it should be able to do very well in all those disturbance patches). Fir also benefited from the increase in disturbances:

  • Absolute basal area decreased strongly under the extreme scenario:

  • Closer look at spruce: its proportion really remains fairly stable under hot-dry climate as long as the disturbance regime doesn’t change much from reference conditions (Dotted red line: simulation with disturbances simulated via modules instead of management)

1.3.3 Trees killed

  • The disturbance modules (black line in baseline facet) kills more trees than our reference disturbance regime (maybe because our assumed severity of 90% of susceptible trees is too low as wind events usually have higher severities?)

  • Basal area killed is very similar between the climate scenarios.

~ the end (for now…) ~